1. Field of the Invention
The present invention is related to a method of error detection for wireless transmission, and more particularly, to a method of error detection using CRC for wireless transmission.
2. Description of the Prior Art
Third generation mobile communication system utilizes a radio receiving method of wideband code division multiple access (WCDMA) and is capable of providing better performance in frequency efficiency, radio coverage, communication quality and transmission speed for multi-media applications. Also, third generation mobile communication system can satisfy different quality of service (QoS) requirements to provide a flexible bi-directional transmission service with better communication quality and low call drop rate.
Since the 3rd generation partnership project (3GPP) has thorough definitions in related specifications, the operations of the broadcast mode and multicast mode are described only briefly hereinafter. The detailed operation of 3G system 3rd Generation Partnership Project (3GPP) has. For universal mobile telecommunications system (UMTS), a third generation mobile communication system includes a user equipment (UE), a UMTS terrestrial radio access network (UTRAN), and a core network (CN). In WCDMA systems, the protocol for radio interface includes physical layer L1, data link layer L2, and network layer L3. Communication protocols for data link layer L2 include access stratum (AS) and non-access stratum (NAS). AS includes multiple sub-layers with various functions, such as radio resource control (RRC), radio link control (RLC), media access control (MAC), packet data convergence protocol (PDCP), broadcast/multicast control (BMC). Data is processed in each sub-layer correspondingly. A service data unit (SDU) is the data received by a sub-layer. A protocol data unit (PDU) is the data transmitted from a sub-layer after processing a received SDU. The receiver and transmitter are configured to process data in opposite directions. Since they are well-known to those skilled in the art, the detailed operations of each sub-layer are described only briefly herein.
The main function of the RLC communication protocol is to perform segmentation, transmission, retransmission and reassembly according to the transmission quality requirement of third generation mobile communication system. In third generation mobile communication system, the transmission quality is graded into four different grades such as conversational, streaming, interactive and background. The RLC operates in three modes to satisfy different transmission quality requirements. The three modes are listed in the following:                1. Transparent mode (TM): The packet data may be directly segmented according to its length without other processing. TM is suitable for real time transmission services, such as voice calls.        2. Unacknowledged mode (UM): In UM, a header is attached to the packet data so that the receiver may check the sequence number of the packet data and to discard erroneous packet data. UM is suitable for services which require both real-time and sequential transmissions, such as voice over Internet protocol (VoIP) or videophone.        3. Acknowledged mode (AM): In addition to segmenting data and attaching header, the receiver is configured to perform sequence check, repetitive check and data re-transmission so as to ensure data accuracy. AM is suitable for a high-accuracy data service such as web browsing, electronic mail, or file transfer.        
Data accuracy and security for both user data and commands need to be guaranteed during radio transmission. The conventional third generation mobile communication system performs encryption on transmitted data using a ciphering method. FIG. 1 is a diagram illustrating encryption and decryption in a conventional third generation mobile communication system. On the left of the dotted line is the transmitter which is configured to generate a plurality of keystream blocks KEYSTREAM by performing F8 algorithm on multiple parameters, such as a ciphering key CK, a count COUNT-C, a bearer identifier BEARER, a direction identifier DIRECTION and a length indicator LENGTH. The transmitter may then generate a ciphered text block CIPHER-TEXT by performing an exclude-OR operation on KEYSTREAM and a plain text PLAIN-TEXT. On the right of the dotted line is the receiver which is configured to perform decryption by performing an exclude-OR operation on KEYSTREAM and the ciphered text block CIPHER-TEXT, thereby recovering the original plain text PLAIN-TEXT.
A wireless communication device is configured to operate in TM during voice communication. The PDU generated after data encryption only include audio data, but no other attached data for verification at the receiver. If there is interference or the transmitter and the receiver are not synchronized, noise may be present during the entire communication process.